improve inferrabilities in Test module (#39761)

* improve inferrabilities in `Test` module

Author: aviatesk

base/show.jl

@@ -2298,7 +2298,7 @@ end
 function print_type_stacktrace(io, type; color=:normal)
     str = sprint(show, type, context=io)
     i = findfirst('{', str)
-    if isnothing(i) || !get(io, :backtrace, false)::Bool
+    if i === nothing || !get(io, :backtrace, false)::Bool
         printstyled(io, str; color=color)
     else
         printstyled(io, str[1:prevind(str,i)]; color=color)

base/stacktraces.jl

@@ -269,8 +269,9 @@ function show(io::IO, frame::StackFrame)
 end
 
 function Base.parentmodule(frame::StackFrame)
-    if frame.linfo isa MethodInstance
-        def = frame.linfo.def
+    linfo = frame.linfo
+    if linfo isa MethodInstance
+        def = linfo.def
         if def isa Module
             return def
         else

stdlib/Test/src/Test.jl

@@ -60,7 +60,7 @@ function scrub_backtrace(bt)
 end
 
 function scrub_exc_stack(stack)
-    return Any[ (x[1], scrub_backtrace(x[2])) for x in stack ]
+    return Any[ (x[1], scrub_backtrace(x[2]::Vector{Union{Ptr{Nothing},Base.InterpreterIP}})) for x in stack ]
 end
 
 # define most of the test infrastructure without type specialization
@@ -259,7 +259,7 @@ end
 
 struct Threw <: ExecutionResult
     exception
-    backtrace
+    backtrace::Union{Nothing,Vector{Any}}
     source::LineNumberNode
 end
 
@@ -551,7 +551,7 @@ function do_test(result::ExecutionResult, orig_expr)
         # The predicate couldn't be evaluated without throwing an
         # exception, so that is an Error and not a Fail
         @assert isa(result, Threw)
-        testres = Error(:test_error, orig_expr, result.exception, result.backtrace, result.source)
+        testres = Error(:test_error, orig_expr, result.exception, result.backtrace::Vector{Any}, result.source)
     end
     isa(testres, Pass) || ccall(:jl_breakpoint, Cvoid, (Any,), result)
     record(get_testset(), testres)